Radio frequency transistor devices may be formed by fabricating a plurality of transistor cells on a semiconductor substrate, e.g., a silicon wafer, with each transistor cell comprising a multiplicity of interdigitated transistor elements connected at common output junctions. The outputs of two or more transistor cells may then be combined to increase the overall power output of the device.
For example, FIG. 1 depicts a radio frequency MOSFET device 10 is formed on a silicon die 12 by connecting the gate terminals 14 and drain terminals 15 of adjacent transistor cells 16 formed on the die 12.
In particular, the transistor cells 16 are successively formed in an alternating, "mirror image" relationship, such that every cell 16 shares either a common gate terminal 14 or common drain terminal 15 with the next adjacent transistor cell 16. Individual conductive paths 18 are formed on one side of the die 12, connecting the respective common gate terminals 14 of each adjacent transistor cell pair, such that all of the gate terminals 14 are connected in series. A further conductive path 20 is formed on an opposite side of the die 12, connecting the respective drain terminals 15 in parallel.
As illustrated in FIG. 2, the gate terminals 14 each "see" a non-terminated impedance in the respective conductive path 18 connecting the adjacent cells 16--i.e., the relative distance of the conductive path 18 between adjacent cells 16 is effectively "infinite". This results in an undesirable push-pull effect between respective transistor cells 16, which, in turn, can cause the device 10 to oscillate and become unstable, especially as the number of interconnected transistor cells 16 is increased in order to increase the overall power output of the device 10.
It would be desirable, therefore, to provide an improved construction for the interconnection of multiple transistor cells to construct radio frequency transistor devices.